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Unformatted text preview: oil is to cool and quench the arc that tends to form when the
circuit is opened. These switches are used for circuits of high voltage and large current carrying
2. Fuses. A fuse is a short piece of wire or thin strip which melts when excessive current flows
through it for sufficient time. It is inserted in series with the circuit to be protected. Under normal
operating conditions, the fuse element it at a temperature below its melting point. Therefore, it
carries the normal load current without overheating. However, when a short circuit or overload
occurs, the current through the fuse element increases beyond its rated capacity. This raises the
temperature and the fuse element melts (or blows out), disconnecting the circuit protected by it. In
* Generally, the load contains reactive elements (inductance and capacitance). The sudden change of current
in the circuit due to breaking results in the production of large induced e.m.f. (several thousand volts)
which ruptures the insulation of air inbetween the contacts, causing a spark. 390
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This note was uploaded on 11/12/2012 for the course MBA 101 taught by Professor Muhannad during the Spring '12 term at Bradford School of Business.
- Spring '12